Certain constraints that are imposed on the engine compartments of automotive vehicles tend to promote the formation of volatile fuel vapor in those components of a fuel injection system which are close to the engine, especially when the engine is hot and not running. These constraints include: smaller, more crowded engine compartments where components are closer to the engine heat and there is less air circulation for removing heat from them; and encasing or shrouding of the engine for noise reduction, protection against road splash, or appearance.
One condition that is rather extreme, but not unusual by any means, is especially conducive to the creation of unwanted fuel vapor in a fuel injector: that condition is referred to as "hot soak", and it occurs in hot temperatures when the vehicle has been left for an extended period of time without the engine running. It is frequently difficult to start the engine under this condition because of fuel vapor that has been created inside the fuel injectors.
Various solutions have been heretofore proposed for overcoming the difficulty of a "hot soak" engine start, but each in one way or another seems to have a disadvantage. A system having bottom feed fuel injectors is much less prone to hot start difficulty because any vapor that does form within the fuel injector does so for the most part at a location that does not obstruct the flow of liquid fuel to the metering orifice. A bottom feed system unfortunately is in general more costly than a top-feed system, and the placement of the metering orifices may be less than optimally related to the desired target point, leaving the potential for undesirable wall wetting by the injections for certain intake geometries.
Other proposed solutions include: running the fuel pump for extended periods of time while the engine is off, running the engine cooling fan, and raising the system fuel pressure, all of which incur added costs and have their own drawbacks.
It has also been proposed to modify individual components, such as reducing the mass of the injector valve body, shrouding the valve body with insulating caps, and molding over the injector body.
The present invention relates to a solution internal to a top-feed fuel injector that enhances the dissipation of hot-start-inhibiting vapor so that a hot engine can be started more quickly with a lesser amount of engine cranking under a hot-start condition. The solution is an economical one since it involves only the modification of the form of an existing part of a fuel injector, namely the adjustment tube that is used to set the bias spring force in a top-feed fuel injector.
The adjustment tube forms a part of the flow path from the inlet through the fuel injector. It has been discovered that the relatively long, narrow nature of the through-hole in the adjustment tube can be prone to sustaining the dome of a vapor bubble that occupies the entire transverse cross-sectional area of the throughhole. In other words, the known geometry of the adjustment tube makes it more difficult to break the surface tension of the vapor bubble, and as a consequence, a bubble, once created, is often difficult to purge through the tube. Vapor in a fuel injector can be purged by flowing out the metering orifice, or it can migrate upwardly, to be replaced by liquid fuel from the fuel supply that feeds pressurized liquid fuel into the top of the fuel injector. Changing the length to diameter ratio of the adjustment tube could alleviate the problem, but such a change could impact adversely on other aspects of the fuel injector construction. Making the length too short could prevent the tube from being satisfactorily crimped to the fuel inlet tube once the adjustment tube has been properly positioned to obtain the desired spring force characteristic; making the diameter larger would increase the overall diametrical dimensions of the fuel injector at a time when the trend is toward smaller and smaller injectors.
The present invention comprises modifying the known adjustment tube by including an axially extending radial slot that runs the full axial length of the adjustment tube so as to interrupt the otherwise full circular diameter of the adjustment tube's through-hole. Importantly, this feature is created without impairing the ability of utilizing the existing technique for axially positioning the adjustment tube within the fuel inlet tube and then crimping the two tubes together once the desired adjustment has been obtained. The invention has the further advantage of being embodied in different structural configurations, several of which will be disclosed herein.
The foregoing, along with further features, advantages, and benefits of the invention, will be seen in the ensuing description and claims that are accompanied by a drawing representing the best mode contemplated at this time for carrying out the invention.